Wildlife Disease II

Contributed Oral Presentations

Contributed paper sessions will be available on-demand for the duration of the conference, then again at the conclusion of the conference.


Mites, Camera, Action: Using Remote Cameras to Estimate the Occurrence of Sarcoptic Mange in Urban Coyotes
Maureen H. Murray; Mason Fidino; Elizabeth W. Lehrer; Seth B. Magle
The distribution of parasites has important implications for wildlife ecology and conservation but is difficult to measure over large spatiotemporal scales. One under-used tool in wildlife disease ecology is remote cameras, typically deployed to monitor wildlife occurrence. We used remote cameras to study the spatiotemporal occurrence of sarcoptic mange in coyotes (Canis latrans). Sarcoptic mange is caused by the mite Sarcoptes scabiei, which induces itching and characteristic lesions of hair loss typically on the tail, hind legs, and ears that can be photographed via remote camera. The energetic costs of mange may explain documented associations between infested canids and anthropogenic resources, especially in winter. In this study, we developed a novel hierarchical occupancy framework to test whether the occurrence of sarcoptic mange in coyotes increases with urbanization or in winter while accounting for the effect of image quality on our ability to detect mange. We used photographs from 113 remote cameras set along transects that extend from the urban core to exurban natural areas. We recorded the presence of visible lesions consistent with sarcoptic mange, a subset of which were validated by a wildlife veterinarian. We analyzed 3971 images of coyotes between Spring 2010 – Winter 2014) and 213 (5%) contained a coyote with mange. While coyote occupancy decreased with urbanization (p<0.05), coyotes with mange were more likely to occur in low-density urban areas (p<0.05). We were more likely to detect mange if the image was in color, not blurry, and if a greater proportion of the coyote was visible. Our results support associations between mange and peri-urban habitats in several canid species but highlight that detecting disease depends on camera placement and the activity patterns of the population of interest. Our approach can advance non-invasive research of visible characteristics of wildlife (e.g. body condition, pregnancy) in many landscapes.
When Host Populations Move North, But Disease Moves South: Counter-Intuitive Impacts of Climate Warming on Disease Dynamics
Elliott Joseph Moran
Climate change is linked to the poleward spread of wildlife ranges and their corresponding diseases. This relationship is supported by countless observations, empirical measurements, and predictions that explore poleward movement in response to a warming climate. We consider an alternative scenario whereby disease moves southward rather than northward in response to climate induced range shifts. This is particularly relevant to viral, bacterial, and prion diseases that do not have thermal tolerance limits and are inextricably linked to their hosts distribution. We formulate a moving habitat integrodifference model with a Susceptible-Infected epidemiological structure for two competing species with different temperature-dependent niche spaces. We present a scenario in which climate change facilitates disease movement southward through space as climate warming moves our niche space northward. There is a tendency to focus on northern latitudes as they generally experience a higher degree of warming relative to southern latitudes; however, our results show that there is a counterintuitive scenario in which southern species may see an increase risk for disease outbreaks and incidence in response to climate change. We explore this in the context of rabies in arctic and red fox. We note the potential for southward spread and further spillover to additional hosts as the disease moves south, presenting an increasing zoonotic threat.
Human Dimensions of Chronic Wasting Disease: A Synthesis and Proposal for Future Wildlife Disease Research
Craig A. Miller; Jerry J. Vaske
Chronic wasting disease (CWD) has been discovered in wild and captive cervids in 26 American states, four Canadian provinces, as well as South Korea, Norway, Finland, and Sweden. Extensive research has examined the pathology and epidemiology of CWD over the past 50 years. Research on the human dimensions (HD) of the disease, however, has only been undertaken during the past 20 years, beginning with the discovery of CWD in Wisconsin and Illinois in 2001. Despite this short timeframe, at least 40 HD studies have been published. Most of this research has explored hunters’ responses to CWD, focused on: (a) intentions to change hunting behavior in response to the disease, (b) perceptions of potential human health risks associated with CWD, (c) concerns about impacts of the disease on deer and elk herds. Studies have also examined hunters’ familiarity and knowledge of CWD, acceptance of management strategies (e.g., testing, incentive programs, herd reduction), and trust in agencies to address the disease. Some research has compared subgroups of hunters (e.g., deer / elk hunters, residents / nonresidents across multiple states) and perceptions of other constituency groups (e.g., non-hunters, landowners, guide outfitters). A few studies have addressed the capacity of agencies to manage CWD and the extent to which agencies use various channels (e.g., internet) to disseminate information about the disease. Finally, researchers have examined current and potential economic impacts of CWD on hunting, wildlife viewing, rural tourism, and the farmed deer and elk industry. This presentation will: (a) synthesize results from these studies, (b) offer suggestions for how these results may inform strategies for managing CWD, and (c) provide directions for future human dimensions research in wildlife disease.
Hunters’ Perceptions of Risk and Hunting Intentions after Emergence of Chronic Wasting Disease in West Tennessee
Abigail Meeks; Neelam Poudyal; Lisa Muller; Chuck Yoest
Chronic Wasting Disease (CWD), a neurological disease affecting the deer and elk populations, was recently discovered in western Tennessee. While it has not yet been shown to spread to humans, stakeholders including the Tennessee Wildlife Resources Agency (TWRA), are interested in understanding whether and how hunters perceive the risk of this disease to deer, cattle, and humans, and to what extent their perception of risk may impact their hunting intentions and behavior. A mixed-mode survey was conducted of licensed hunters in western Tennessee at the beginning of the 2019 deer hunting season. Results from 1,674 respondents (response rate = 33.48%) showed that while almost all hunters (99%) in the region are aware of CWD, the majority (65.68%) are concerned that little is currently known about CWD and its impact on humans. About half of hunters (49%) agreed that appropriate actions have been taken to prevent its spread. In terms of its risk hunters were most concerned with CWD spreading throughout Tennessee (74.80%) and the deer population dramatically declining (47.52%). Regarding their future hunting intentions, 26.51% hunters indicated to either substantially or slightly decrease their hunting in CWD positive counties. While hunters generally supported all management actions to control CWD, relatively higher levels of acceptability were found for requiring hunters to provide a sample for testing (52%) and requiring unused deer parts to be buried, incinerated, or disposed in a landfill (35%), compared to the lower support for doing nothing and letting nature take its course (7%). Results shed light on how hunters view the risk of CWD and how they are willing to change their hunting behavior and will be useful to stakeholders including TWRA in determining future management actions as they relate to CWD management.
Evaluating the Complexity and Uncertainty Associated with Management of Chronic Wasting Disease
Noelle E. Thompson; David M. Williams; William F. Porter
Despite efforts to control chronic wasting disease (CWD) for the past three decades, persistent uncertainties and complexities associated with the ecology of this disease continue to limit our understanding of and our ability to discern management solutions. Agent-based modeling (ABM) provides a modeling framework that allows us to simulate the complexity inherent to wildlife disease systems and can manage the uncertainties associated with CWD and its management. Using this framework, our objective was to evaluate a suite of localized management strategies using a stochastic and spatially explicit agent-based epidemiological model. This model projects population and disease dynamics for free-ranging white-tailed deer (Odocoileus virginianus) herds in the state of Michigan. Management strategies assessed in this study include spatially and temporally explicit culling, hunter-harvest programs, and a number of integrated management plans using combinations of these techniques. To address the uncertainties associated with management of CWD, we assess these strategies using a range of public compliance and agency success rates. Specifically, we tested localized culling associated with removal success rates of 60, 75, 90, and 100% of deer within a designated removal area. We also modeled the effects of antler point restrictions associated with 75, 90, and 100% rates of compliance by hunters. Our results indicate that rates of compliance and agency success affect whether a management strategy is determined to be effective (reduces transmission and/or eliminates the disease). Without high levels of cooperation by hunters and success by agency personnel, intervention is unlikely to be impactful for CWD.
Putting Out the Fire: A Review of Wildlife Agency Responses to Chronic Wasting Disease
Miranda HJ Huang; Noelle E. Thompson; Sonja A. Christensen; Stephen Demarais
Chronic wasting disease has been spreading throughout free-ranging cervids in North America since its discovery in the 1960s. This prion disease is unlike any other wildlife disease state agencies have ever had to manage and the learning curve has been steep. With 26 US states and two Canadian provinces historically or presently positive for CWD in free-ranging cervids, a plethora of management experience exists. Despite the potential value of this acquired knowledge, a synthesis is lacking. We reviewed approaches by state/provincial agencies and their resultant effects. US states and Canadian provinces have been finding CWD in free-ranging cervid herds since 1981. So far, the year with the most states/provinces finding CWD in a free-ranging captive for the first time is 2002 (4 states), which corresponds with the year US Congress started providing states with large funds to support CWD responses. The next most common years for initial CWD discovery in free-ranging cervids was 2005 (2 states, 1 province) and 2012 (3 states). The most common surveillance technique used to find the first positive in a state was hunter harvest (16), followed by suspect clinicals (9), targeted sampling in a high-risk area (2), and road killed deer (1). Hunter-harvest surveillance is cost efficient and effective. The number of states and provinces that had their first CWD positive in a free-ranging deer (15) was only slighter higher than the number that first detected in a captive cervid (13), which emphasizes the importance of sampling both populations. We expound on four phases of response by wildlife agencies to CWD: prior to disease detection, initial detection, initial response, and altered response. This synthesis of past responses by government wildlife agencies to CWD and known outcomes can provide guidance for future management of CWD.
Changes in Chronic Wasting Disease Ecology in Elk at Rocky Mountain National Park
Nathan L. Galloway; Jenny G. Powers; Ryan J. Monello; Margaret A. Wild
We conducted two key studies at Rocky Mountain National Park, Colorado, to investigate the population-level effects of chronic wasting disease (CWD) in elk (Cervus elaphus nelsoni) with historically high densities (up to 110 elk/sq km on portions of the winter range). CWD was first detected in this population in 1981 and by the early 2000’s half of the adult elk found dead tested positive for CWD. We estimated disease prevalence of ~13% (8-19%; n=136) in adult females in 2008. Additionally, we estimated that the population growth rate in female elk was flat (λ~1.0) and that CWD can reduce adult female survival and decrease population growth rate of elk (Monello et al. 2014). In a subsequent study, we investigated disease dynamics in the elk population and monitored changes in disease transmission pressure associated with locally specific reduced elk density and increased elk dispersion. We now estimate prevalence for 2012-2016 of ~8.5% (4.6-13.3%; n=138). Results corroborate that CWD reduces adult female elk survival and this increased mortality decreases the population growth rate. Concurrent with our study, elk are re-distributing to lower elevations outside of the park, where CWD prevalence has always been lower, resulting in much lower densities within the park. The effects of this on CWD prevalence are unclear; movement may simply spatially dilute disease across the landscape or lower densities may reduce disease transmission.
Modeling Epidemic Outcomes and Prevention Strategies for Introduced Pathogens in An Isolated Carnivore
Jessica N. Sanchez; Brian R. Hudgens
Disease transmission and epidemic prevention are top conservation concerns for wildlife managers, especially for small, isolated populations. Previous studies have shown that the course of an epidemic within heterogeneous host populations is strongly influenced by whether pathogens are introduced to areas of relatively high or low host densities. We tested how disease monitoring and vaccination programs are influenced by spatial heterogeneity in host distributions by developing a spatially-explicit model, parameterized by field studies, simulating the spread of rabies and canine distemper in a spatially heterogeneous population of Channel Island foxes (Urocyon littoralis). Introductions into areas of high fox densities resulted in faster transmission and greater population reductions for both pathogens, compared to introductions to low fox density sites. When introduced to low fox density sites, rabies was >5x more likely to go locally extinct compared to high-density introductions, leaving an average of >99% of foxes uninfected. Canine distemper went extinct in >98% of simulations regardless of fox density at the site of introduction, but only after >90% of foxes were infected. Increasing the monitoring frequency of radio-collared foxes reduced the time to epidemic detection and percentage of foxes infected for both pathogens compared to increasing the number of collared foxes. The efficacy of vaccination was heavily influenced by local fox density at the site of pathogen introduction. A vaccine firewall far away from the site of pathogen introduction was generally the least effective strategy compared to a firewall close to the site of pathogen introduction or a random distribution of vaccines across the island. Our results highlight the challenges in mitigating an epidemic of novel disease in a naïve host population, in part due to complex interactions between pathogen biology and host behavior, exacerbated by the spatial variation of most host populations.


Contributed Oral Presentations
Location: Virtual Date: Time: -